This invention relates generally to the construction of valves for controlling fluid flow.
Conventional valves such as are employed for controlling flow of liquids and gases employ a body having flow passages and a valve seat located between the passages. A valve assembly is adapted to be moved from an open or retracted position spaced from the seat to a closed position in sealing engagement with the seat. The sealing surfaces of the seat may be flat or conical shaped. The movable valve assembly may be constructed to have metal-to-metal sealing engagement with the seat, or it may have a member of resilient material (e.g., natural or synthetic rubber or elastomer) adapted to engage the seating surfaces to provide a seal. Such a valve is subject to deterioration due to damage that may occur to the resilient member. For example, the resilient sealing member may become permanently distorted, worn or mutilated in such a manner as to prevent an effective seal. Some valves have been constructed with cylindrical seating surfaces and with a movable valve assembly which has a resilient member that engages the cylindrical seating surface for closed valve position. Such valves likewise have disadvantages, including wear of the resilient parts in operating the valve, and constructions that are relatively expensive to manufacture.